Various types of Analog-to-Digital Converter (ADC) circuits are well known in the art. One type of ADC is the sigma-delta or delta-sigma ADC. In general, a sigma-delta ADC includes a sigma delta modulator (SDM) and a digital filter. The sigma delta ADC oversamples an analog input signal and generates a bit stream output having an average value that tracks the analog input.
As is known in the art, to enable recovery an input signal must be sampled at a rate equal to or greater than the Nyquist frequency Fs, i.e., at least twice the bandwidth of the input signal. The frequency spectrum of the digitized signal contains the spectrum of the analog input signal along with quantization noise from DC to Fs/2 resulting from the conversion of an analog input signal having an infinite number of states to a digital signal having a fixed number of states. The number of states corresponds to the resolution of the ADC.
In this arrangement, the noise envelope is generally flat. To increase the Signal to Noise Ratio (SNR), the sampling rate can be increased (oversampling), such as by a ratio k, i.e., kFS, to lower the noise floor since the noise is spread over a relatively large frequency range. To further increase the SNR, noise-shaping techniques can be used to push out the noise to higher frequencies. Oversampling can provide a gain of at least 6 dB for each factor of four times oversampling.
SDM ADCs have a variety of coefficients that define the operating characteristics of the circuit. These coefficients can be problematic when attempting to provide programmable ADCs having optimal performance characteristics and flexibility over a range of parameters, such as OSR.